The term employs traditional light-versus-darkness imagery to contrast the era's "darkness" (lack of records) with earlier and later periods of "light" (abundance of records). The concept of a "Dark Age" originated in the 1330s with the Italian scholar Petrarch, who regarded the post-Roman centuries as "dark" compared to the light of classical antiquity. The phrase "Dark Age" itself derives from the Latin saeculum obscurum, originally applied by Caesar Baronius in 1602 to a tumultuous period in the 10th and 11th centuries. The concept thus came to characterize the entire Middle Ages as a time of intellectual darkness between the fall of Rome and the Renaissance; this became especially popular during the 18th-century Age of Enlightenment.

As the accomplishments of the era came to be better understood in the 18th and 20th centuries, scholars began restricting the "Dark Ages" appellation to the Early Middle Ages (c. 5th–10th century). The majority of modern scholars avoid the term altogether due to its negative connotations, finding it misleading and inaccurate. The original definition remains in popular use, and popular culture often employs it as a vehicle to depict the Middle Ages as a time of backwardness, extending its pejorative use and expanding its scope.

The term was originally intended to denote an intermediate period between Classical Antiquity and the Modern era. In the 19th century scholars began to recognize the accomplishments of the period, which challenged the image of a time exclusively of darkness and decay. Nowadays the term is not used by scholars to refer to the entire medieval period; when used, it is generally restricted to the Early Middle Ages.

The rise of archaeology in the 20th century has shed light on the period, offering a more nuanced understanding of its achievements. Other terms of periodization have come to the fore: Late Antiquity, the Early Middle Ages, and the Great Migrations, depending on which aspects of culture are being emphasized. Today, on the rare occasions when the term is used by historians, it is intended to be neutral and express the idea that the period often seems 'dark' from the scarcity of historical record, and artistic and cultural output.

The idea of a Dark Age originated with the Tuscan scholar Petrarch in the 1330s. Writing of the past, he said: "Amidst the errors there shone forth men of genius; no less keen were their eyes, although they were surrounded by darkness and dense gloom".Christian writers, including Petrarch himself, had long used traditional metaphors of 'light versus darkness' to describe 'good versus evil'. Petrarch was the first to give the metaphor secular meaning by reversing its application. He now saw Classical Antiquity, so long considered a 'dark' age for its lack of Christianity, in the 'light' of its cultural achievements, while Petrarch's own time, allegedly lacking such cultural achievements, was seen as the age of darkness.